CN110837116B - Method for determining operation upper limit pressure of salt cavern gas storage - Google Patents
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- 239000003345 natural gas Substances 0.000 abstract description 10
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
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- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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- G01V2210/00—Details of seismic processing or analysis
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Abstract
The invention discloses a method for determining the operation upper limit pressure of a salt cavern gas storage, and belongs to the technical field of petroleum and natural gas. The method comprises the following steps: determining a target operation upper limit pressure; monitoring the actual operating pressure of the salt cavern gas storage; injecting gas into the salt cavern gas storage, and gradually increasing the actual operating pressure of the salt cavern gas storage to a target operating upper limit pressure; carrying out microseism monitoring through a monitoring well to obtain the number of microseism events occurring every day in a first pressure lifting stage and the number of microseism events occurring every day in a second pressure lifting stage; comparing the average number of microseismic events occurring per day n during the first pressure build-up phase1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2(ii) a When n is2And n1When the ratio of (A) to (B) is less than a preset value, determining the upper limit pressure of the operation of the salt cavern gas storage as P1Thereby improving the storable amount of the salt cavern gas storage.
Description
Technical Field
The invention relates to the technical field of petroleum and natural gas, in particular to a method for determining the operation upper limit pressure of a salt cavern gas storage.
Background
Salt cavern reservoirs are caverns formed in underground salt formations that can be used to store natural gas.
When the salt cavern gas storage is built, an injection-production well with the depth reaching the salt layer is usually drilled, and then a cavity is built through water to form the cavern in the salt layer. Each salt cavern gas storage is provided with an operation upper limit pressure, and in the production process of the salt cavern gas storage, the operation pressure of the salt cavern gas storage cannot exceed the operation upper limit pressure, so that the production safety of the salt cavern gas storage is ensured.
For the same salt cavern gas storage, the larger the operation upper limit pressure is, the larger the amount of the natural gas which can be stored is. According to the existing standard, the upper limit pressure of the operation of the salt cavern gas storage does not exceed 80% of the minimum principal stress, and for safety reasons, in the actual setting, the upper limit pressure of the operation of the salt cavern gas storage is much lower than 80% of the minimum principal stress, so that the storable amount of the salt cavern gas storage is small.
Disclosure of Invention
The embodiment of the invention provides a method for determining the operation upper limit pressure of a salt cavern gas storage, which is used for improving the storable amount of the salt cavern gas storage. The technical scheme is as follows:
the embodiment of the invention provides a method for determining the operation upper limit pressure of a salt cavern gas storage, which comprises the following steps:
determining a target operating upper limit pressure P of a salt cavern gas storage1，P2≤P1≤P0，P0Is the theoretical upper limit pressure, P, of operation of the salt cavern gas storage2The current operation upper limit pressure of the salt cavern gas storage is set;
monitoring the actual operating pressure of the salt cavern gas storage;
injecting gas into the salt cavern gas storage until the actual operation pressure of the salt cavern gas storage is gradually increased to the target operation upper limit pressure P1；
Performing microseismic monitoring through a monitoring well to obtain a first pressure boost stepThe number of the micro-seismic events occurring every day in the section and the number of the micro-seismic events occurring every day in a second pressure increasing stage, wherein the first pressure increasing stage is from the actual operating pressure of the salt cavern gas storage to P2The second pressure raising stage is that the actual operating pressure of the salt cavern gas storage is from P2Increase to P1The depth of the monitoring well reaches a salt layer where the salt cavern gas storage is located;
comparing the average number of microseismic events per day n occurring during the first pressure rise period1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2；
When n is2And n1When the ratio of (A) to (B) is less than a preset value, determining the upper limit pressure of the salt cavern gas storage operation as P1。
Optionally, the microseismic monitoring through the monitoring well comprises:
arranging multistage three-component detectors in the monitoring well, wherein the multistage three-component detectors are distributed upwards at equal intervals from the bottom of the monitoring well;
and monitoring the microseism event through the multistage three-component detector.
Optionally, injecting gas into the salt cavern gas storage until the operating pressure of the salt cavern gas storage is gradually increased to a target upper operating limit pressure P1The method comprises the following steps:
raising the actual operating pressure of the salt cavern reservoir to P at a first rate during the first pressure raising phase2；
Raising the actual operating pressure of the salt cavern reservoir at a second rate from P in the second pressure-raising phase2Is lifted to P1The first speed is greater than the second speed.
Optionally, the ratio of the first speed to the second speed is 2-3.
Optionally, the monitoring of the actual operating pressure of the salt cavern gas storage comprises:
monitoring the wellhead gas injection pressure of the salt cavern gas storage;
and acquiring the gas column pressure of the salt cavern gas storage, and taking the sum of the wellhead gas injection pressure and the gas column pressure as the operating pressure of the salt cavern gas storage.
Optionally, the preset value is greater than 100% and less than 110%.
Alternatively, the theoretical upper operating limit pressure is determined in the following manner:
carrying out an earth stress test in an injection well of the salt cavern gas storage;
determining the relation between the minimum principal stress and the formation depth according to the data obtained by the geostress test;
and determining the theoretical operation upper limit pressure of the salt cavern gas storage according to the relation between the minimum principal stress and the formation depth.
Optionally, the performing geostress testing in an injection and production well of the salt cavern gas reservoir comprises:
and acquiring the minimum principal stress of a plurality of depth positions by adopting a hydraulic fracturing method.
Optionally, the determining a relationship between the minimum principal stress and the formation depth according to the data obtained from the geostress test includes:
and fitting a relation curve of the minimum principal stress and the depth according to the depth values of the plurality of depth positions and the minimum principal stress of the plurality of depth positions.
Optionally, before performing microseism monitoring through the monitoring well to obtain the number of microseism events occurring each day in the first pressure rise period and the number of microseism events occurring each day in the second pressure rise period, the method further includes:
recording the position of each occurrence of the micro-seismic event in a plane coordinate mode, judging whether the micro-seismic event is caused by the increase of the pressure in the salt cavern gas storage, and removing the micro-seismic event when the micro-seismic event is not caused by the increase of the pressure in the salt cavern gas storage.
The technical scheme provided by the embodiment of the invention has the beneficial effects that at least: performing micro-seismic monitoring through the monitoring well, injecting gas into the salt cavern gas storage,gradually increasing the actual operating pressure of the salt cavern gas storage to the target operating upper limit pressure P1(ii) a The microseismic monitoring can acquire the number of microseismic events occurring in the process of injecting gas into the salt cavern gas storage. By comparing the average number of microseismic events occurring per day n during the first pressure build-up phase1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2The first pressure raising stage is that the actual operating pressure of the salt cavern gas storage is increased to P2The second pressure raising stage is that the actual operating pressure of the salt cavern gas storage is from P2Increase to P1When n is equal to2And n1When the ratio of (A) to (B) is less than a preset value, the number of the microseismic events is not counted from P along with the operation pressure2Increase to P1And the concentrated occurrence proves that the mechanical properties of the cavity top and the surrounding rock of the salt cavern gas storage are stable, the phenomena of cracking or cavity wall block falling do not occur, and the target operation upper limit pressure which is higher than the current operation upper limit pressure can be used as the operation upper limit pressure of the salt cavern gas storage, so that the storable amount of the salt cavern gas storage is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method for determining an upper operating pressure limit for a salt cavern gas storage according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a salt cavern gas storage provided in an embodiment of the present invention;
FIG. 3 is a chart of a trace record of microseismic events provided by an embodiment of the present invention;
FIG. 4 is a distribution plot of microseismic events provided by embodiments of the present invention;
FIG. 5 is a flow chart of a method for determining a theoretical upper operating limit pressure for a salt cavern gas storage according to an embodiment of the invention;
fig. 6 is a flowchart of a method for establishing a salt cavern gas storage according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Fig. 1 is a flowchart of a method for determining an upper limit pressure of operation of a salt cavern gas storage according to an embodiment of the present invention. As shown in fig. 1, the method includes:
s11: determining a target operating upper limit pressure P of a salt cavern gas storage1。
In particular, P2≤P1≤P0，P0Is the theoretical upper limit pressure, P, for operation of the salt cavern gas storage2The current operation upper limit pressure of the salt cavern gas storage is obtained.
According to the existing standard (national salt cavern gas storage standard Z341Series-14 of canada), the salt cavern gas storage operation upper limit pressure does not exceed 80% of the minimum principal stress. Fig. 2 is a schematic structural diagram of a salt cavern gas storage provided in an embodiment of the present invention. As shown in fig. 2, the minimum principal stress is the minimum principal stress of the formation where the shoes 11a of the technical casing 11 are located in the injection and production well of the salt cavern gas storage. The minimum principal stress may be obtained by geostress testing while drilling an injection and production well.
Current operation upper limit pressure P2The operation upper limit pressure is set at present in the salt cavern gas storage, and is usually set according to experience and can be usually set to be 80% -95% of the theoretical operation upper limit pressure. The current operation upper limit pressure may be set to 17Mpa, for example, when the theoretical operation upper limit pressure is 18.22 Mpa. In order to ensure the safety of the salt cavern gas storage, a large margin is left for the current operation upper limit pressure. Due to the empirically set current operating upper limit pressure P2Much less than the theoretical upper operating limit pressure, which reduces the amount of salt cavern storage that can be stored. The purpose of this embodiment is to increase the upper limit pressure of the salt cavern gas storage under the condition of ensuring the safety of the salt cavern gas storage, so as to increase the salt cavern gas storageStorable amount of gas reservoir.
Can be at the current operation upper limit pressure P2On the basis of the target pressure, 0.1-0.8 MPa is added to obtain the target operation upper limit pressure P1. The performance of the compressor of the injection and production station can be set, and the overlarge target operation upper limit pressure P1The performance of the compressor may not be satisfied, and from the viewpoint of safe production, it is preferable that the upper limit pressure P may be set at the current operation2On the basis of the pressure difference, 0.1MPa to 0.5MPa is added.
S12: and monitoring the actual operating pressure of the salt cavern gas storage.
The step S12 may include:
firstly, monitoring the wellhead gas injection pressure of the salt cavern gas storage. Wherein, well head gas injection pressure can acquire through the well head gas injection manometer of well head.
And secondly, acquiring the gas column pressure of the salt cavern gas storage, and taking the sum of the gas injection pressure of the wellhead and the gas column pressure as the actual operating pressure of the salt cavern gas storage.
Since the technical casing 11 in the injection and production well of the salt cavern gas storage also contains natural gas, and the length of the technical casing 11 is usually hundreds of meters, the natural gas column of the part generates larger pressure, for example, in the technical casing 11 of 996.18m, the pressure of the gas column generated by the natural gas column is 1.2 MPa. The actual operation pressure is the gas pressure at the pipe shoe of the technical sleeve in the injection and production well of the salt cavern gas storage, the gas pressure at the position is inconvenient to directly measure, and the sum of the wellhead gas injection pressure and the gas column pressure is equal to the actual operation pressure, so that the actual operation pressure is calculated through the wellhead gas injection pressure and the gas column pressure, and the acquisition method is simple.
S13: injecting gas into the salt cavern gas storage until the actual operation pressure of the salt cavern gas storage is gradually increased to the target operation upper limit pressure P1。
When the pressure is increased, the pressure can be increased by two pressure increasing stages, namely a first pressure increasing stage and a second pressure increasing stage, wherein the actual operation pressure of the salt cavern gas storage is increased to P in the first pressure increasing stage2The second pressure raising stage is the actual operating pressure of the salt cavern gas storageForce from P2Increase to P1And (3) a stage of (a).
Alternatively, the step S13 may include:
in a first pressure raising phase, raising the actual operating pressure of the salt cavern gas storage to P at a first speed2。
In a second pressure raising stage, raising the actual operating pressure of the salt cavern gas storage from P at a second speed2Is lifted to P1The first speed is greater than the second speed.
Optionally, the ratio of the first speed to the second speed may be 2-3. For example, the first speed can be 0.2-0.3 MPa/day, the second speed can be set to be 0.1 MPa/day, in the second pressure increasing stage, the actual operating pressure of the salt cavern gas storage is larger than the target operating upper limit pressure, the second speed is set to be slower, safe production can be ensured, and accidents caused by the fact that the pressure increasing speed is too large are avoided.
Referring again to fig. 2, a technical casing 11, an outer casing 12 and an inner casing 13 are inserted into the wellbore of the salt cavern gas storage. Here, the technical sleeve 11 is arranged outside the outer sleeve 12, so that an annular space is formed between the technical sleeve 11 and the outer sleeve 12. The outer sleeve 12 is sleeved outside the inner sleeve 13, so that an annular space is formed between the outer sleeve 12 and the inner sleeve 13. At the wellhead there are valves 33 which can open and close the inner casing 13, valves 32 which can open and close the annulus between the inner casing 13 and the outer casing 12, and valves 31 which can open and close the annulus between the technical casing 11 and the outer casing 12. When injecting natural gas, the valve 31 of the technical casing 11 and the valve 32 of the outer casing 12 at the wellhead can be closed, and the valve 33 of the inner casing 13 can be opened to inject the natural gas from the inner casing 13.
Because the difference between the actual operating pressure and the wellhead gas injection pressure is fixed and is always the gas column pressure generated by the natural gas column, the wellhead gas injection pressure can be monitored in the first pressure lifting stage and the second pressure lifting stage so as to ensure that the actual operating pressure is lifted to P2And P1。
Illustratively, the current upper operating limit pressure P for a particular salt cavern gas reservoir217MPa, target upper operating limitPressure P1Is 17.5 MPa. The current wellhead gas injection pressure of the salt cavern gas storage is 13.98MPa, and the gas column pressure is 1.2 MPa. And in the first pressure lifting stage, the wellhead gas injection pressure is lifted to 15.8MPa, the actual operating pressure of the salt cavern gas storage reaches 17MPa when the first pressure lifting stage is finished, in the second pressure lifting stage, the wellhead gas injection pressure is lifted to 16.3MPa, and the actual operating pressure of the salt cavern gas storage reaches 17.5MPa when the second pressure lifting stage is finished.
S14: and carrying out microseism monitoring through the monitoring well to obtain the number of microseism events occurring every day in the first pressure lifting stage and the number of microseism events occurring every day in the second pressure lifting stage.
For example, a monitoring well with the depth reaching the salt deposit where the salt cavern gas storage is located can be drilled, and micro-seismic monitoring is carried out through the monitoring well.
The distance between the monitoring well and the injection and production well can be within 800m, and the monitoring accuracy of the microseism event monitoring is reduced when the monitoring well is too far away from the injection and production well. Since the salt cavern gas reservoirs are usually centrally located, the monitoring well may be an injection-production well of another salt cavern gas reservoir being built around the salt cavern gas reservoir.
In the embodiment, a plurality of stages of three-component detectors are arranged in the monitoring well, and the plurality of stages of three-component detectors are distributed upwards at equal intervals from the bottom of the monitoring well. Microseismic monitoring through the monitoring wells may include monitoring microseismic events through a multi-stage three-component detector.
As shown in fig. 2, a monitoring well 40 is drilled near the salt cavern reservoir. Illustratively, the monitoring well 40 has a technical casing (not shown) running deep (i.e., a run-in depth, which refers to the depth to which the technical casing is run into the formation) 998.4m with a three-component geophone 41 disposed within the range of depths 870m to 980 m. The lower depth of a technical casing in the injection and production well is 996.18m, so that the three-component detector 41 is arranged to be close to the salt layer 21 where the salt cavern gas storage is located, and meanwhile, the three-component detector 41 can be prevented from entering an open hole section and being influenced by stones falling from the well wall.
Alternatively, 12-stage three-component detectors may be provided at a pitch of 10m, with only 3-stage three-component detectors being shown in fig. 2 by way of example.
When a three-component detector is used for monitoring a microseismic event, the sampling interval can be 0.5ms, the recording length can be 10s, and the gain can be 40 dB.
The increase of the actual operating pressure of the salt cavern gas storage may cause the phenomena of the rupture of a cavity top or surrounding rock, the falling of a cavity wall block and the like, thereby affecting the stability and the sealing property of the salt cavern gas storage. Meanwhile, normal phenomena such as rock fracture and the like also exist in the stratum, and the microseism caused by the phenomena can be recorded through microseism monitoring, so that the times of the phenomena such as cavity top or surrounding rock fracture, cavity wall block falling, rock fracture and the like in the stratum can be known.
Specifically, the number of the micro-seismic events per day in the whole micro-seismic monitoring process can be recorded in a form of a chart. Fig. 3 is a chart of recording the number of micro-seismic events, in which a bar chart records the number of micro-seismic events occurring each day from 10 month 8 to 11 month 1, wherein no micro-seismic event occurs in four days of 10 month 27, 10 month 28, 10 month 30 and 11 month 1. The curve records the wellhead pressure detected each day. No. 10 and No. 12 are the starting time of the first pressure increasing stage, the number of the micro-seismic events occurring in the day is 38, the wellhead pressure is 14MPa, No. 10 and No. 20 are the ending time of the first pressure increasing stage, the number of the micro-seismic events occurring in the day is 4, the wellhead pressure is 15.8MPa, No. 10 and No. 25 are the ending time of the second pressure increasing stage, the number of the micro-seismic events occurring in the day is 8, and the wellhead pressure is 16.3 MPa.
S15: comparing the average number of microseismic events occurring per day n during the first pressure build-up phase1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2。
By comparing the average number of the micro-seismic events occurring every day in the first pressure lifting stage and the second pressure lifting stage, whether the second pressure lifting stage causes the concentrated occurrence of the micro-seismic events can be known, and whether the current operation upper limit pressure can be determined from P2Lifting to targetUpper limit pressure P1。
S16: when n is2And n1When the ratio of (A) to (B) is less than a preset value, determining the upper limit pressure of the operation of the salt cavern gas storage as P1。
Alternatively, the preset value may be greater than 100% and less than 110%. Due to the higher pressure in the second pressure rise stage, fewer micro-seismic events are typically caused during the pressurization process, as long as n is2And n1The ratio of (A) to (B) is within a preset value range, and the salt cavern gas storage can be considered to be capable of normally producing. The preset value is preferably 105% to further ensure the reliability and safety of the salt cavern gas storage.
If n is2And n1Is more than a preset value, it indicates a target operation upper limit pressure P1Too high, the target operation upper limit pressure P may be slightly lowered1。
Carrying out micro-seismic monitoring through the monitoring well, injecting gas into the salt cavern gas storage, and gradually increasing the actual operating pressure of the salt cavern gas storage to the target operating upper limit pressure P1(ii) a The number of micro-seismic events occurring in the process of injecting gas into the salt cavern gas storage can be obtained through micro-seismic monitoring. By comparing the average number of microseismic events occurring per day n during the first pressure build-up phase1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2The first pressure raising stage is that the actual operating pressure of the salt cavern gas storage is increased to P2The second pressure raising stage is that the actual operating pressure of the salt cavern gas storage is from P2Increase to P1When n is equal to2And n1When the ratio of (A) to (B) is less than a preset value, the number of the microseismic events is not counted from P along with the operation pressure2Increase to P1And the concentrated occurrence proves that the mechanical properties of the cavity top and the surrounding rock of the salt cavern gas storage are stable, the phenomena of cracking or cavity wall block falling do not occur, and the target operation upper limit pressure which is higher than the current operation upper limit pressure can be used as the operation upper limit pressure of the salt cavern gas storage, so that the storable amount of the salt cavern gas storage is improved.
Optionally, after step S14, the location of each micro-seismic event may be recorded in planar coordinates, and the micro-seismic event may be determined to be due to an increase in pressure in the salt cavern gas, and removed when the micro-seismic event is not due to an increase in pressure in the salt cavern gas. FIG. 4 is a distribution diagram of a microseismic event wherein well B is an injection and production well, well A is a monitor well, and wells C1 and C2 are two additional wells around the injection and production well, according to an embodiment of the present invention. It can be seen from the profiles that microseismic events 50 occur primarily between the C1 wells and the C2 wells. Whether the micro-seismic event is caused by geostress adjustment at the location of the natural fault can be inferred from the location where the micro-seismic event occurred. For example, from geological exploration data, it was found that natural fractures exist between the C1 well and the C2 well, and it can be inferred that much of the microseismic events are due to rock fractures caused by stress adjustment at the location of the natural fractures. If the microseismic event occurred primarily around the B-well, it is an indication that the microseismic event is likely due to an increase in pressure within the salt cavern reservoir, requiring a decrease in pressure within the salt cavern reservoir. By recording the position of each occurrence of the micro-seismic event, judging whether the micro-seismic event is caused by the increase of the pressure in the salt cavern gas storage, all the micro-seismic events which are irrelevant to the salt cavern gas storage can be removed, so that the micro-seismic events which are relevant to the salt cavern gas storage are represented by n1 and n2, the reliability of the determination method can be improved, and the safety of the salt cavern gas storage is ensured.
The method for determining the upper limit pressure of the operation of the salt cavern gas storage shown in fig. 1 can be applied to the salt cavern gas storage already put into operation to improve the upper limit pressure of the operation of the salt cavern gas storage. When the salt cavern gas storage is established, the theoretical operation upper limit pressure of the salt cavern gas storage is obtained through geological exploration, so that the theoretical operation upper limit pressure of the salt cavern gas storage can be obtained from existing geological exploration data.
The method for determining the upper limit pressure of the operation of the salt cavern gas storage shown in the figure 1 is also suitable for the newly built salt cavern gas storage. In the process of building the salt cavern gas storage, the theoretical operation upper limit pressure of the salt cavern gas storage needs to be obtained through geological exploration, and fig. 5 is a flow chart of the method for determining the theoretical operation upper limit pressure of the salt cavern gas storage provided by the embodiment of the invention. As shown in fig. 5, the method includes:
s21: and carrying out an earth stress test in the injection and production well.
The injection and production wells can be drilled according to the depth of the cavitating salt layer section.
When constructing a salt cavern reservoir, it is often necessary to determine the depth of the cavitating salt interval in order to determine the length of the technical casing to be drilled in the injection-production well. For example, if a cavity needs to be created in a salt layer with a depth of 1011.4m to 1132m, a 996.18m technical casing can be placed in the injection and production well.
Alternatively, hydraulic fracturing may be used to obtain the minimum principal stress at multiple depth locations. The hydraulic fracturing test creates a tensile fracture at the test horizon and extends the fracture into the virgin formation beyond the wellbore reach, which will close as the pressure drops after stopping fluid injection. And analyzing the pressure drop curve by a geomechanics and transient seepage theoretical method to obtain the fracture closing pressure. The fracture closure pressure is equivalent to the minimum principal stress of the formation. The minimum principal stress of different depth positions can be accurately obtained by a hydraulic fracturing method.
After the injection and production well is drilled, a plurality of depth positions can be selected for hydraulic fracturing, for example, a cavity needs to be built in a salt layer with the depth of 1011.4 m-1132 m, and 5 positions with the depths of 1127.0 m-1128.4 m, 1110.0 m-1111.4 m, 1091.5 m-1092.9 m, 1080.5 m-1082.9 m and 1048.0 m-1049.4 m can be respectively subjected to hydraulic fracturing to obtain the minimum main stress of the corresponding positions.
S22: and determining the relation between the minimum principal stress and the depth of the stratum according to the data obtained by the geostress test.
In particular, a minimum principal stress versus depth curve may be fitted based on the depth values of the plurality of depth positions and the minimum principal stress of the plurality of depth positions. The minimum principal stress of different depth positions can be predicted through the fitted relation curve.
Taking the minimum principal stresses obtained by hydraulic fracturing at the above-mentioned 5 positions as an example, the minimum principal stresses at the 5 positions obtained in S21 are 25.59MPa, 24.97MPa, 24.78MPa, 24.53MPa, and 23.77MPa, respectively, and the equation for obtaining the fitted relationship curve is as follows:
y＝0.02183x+1.03424 (1)
where y is the minimum principal stress and x is the depth.
S23: and determining the theoretical operation upper limit pressure of the salt cavern gas storage according to the relation between the minimum principal stress and the depth of the stratum.
Step S23 may specifically include:
and determining the minimum principal stress of the stratum where the technical casing shoe is located according to the relation between the minimum principal stress and the depth of the stratum.
According to the formula (1), the minimum principal stress at the shoe of the technical casing (depth 996.18m) was 22.78 MPa.
And taking 70-80% of the minimum principal stress of the stratum where the pipe shoe of the technical casing is positioned as the theoretical operation upper limit pressure.
According to the existing standards, the upper limit operating pressure of the salt cavern gas storage does not exceed 80% of the minimum principal stress, and the theoretical upper limit operating pressure is usually set to 70% to 80% of the minimum principal stress from the viewpoint of safety. Illustratively, the theoretical upper operating limit pressure is 18.22MPa, for example, 80% of the minimum principal stress.
Fig. 6 is a flowchart of a method for establishing a salt cavern gas storage according to an embodiment of the present invention. After the theoretical operating upper limit pressure of the salt cavern gas storage is determined, the salt cavern gas storage can be built by the following method. As shown in fig. 6, the method includes:
s31: and (4) carrying out water dissolution and cavity building through the injection and production well to form a salt cavern.
The water-soluble cavity construction generally has two modes of positive circulation cavity construction and reverse circulation cavity construction, wherein the positive circulation cavity construction means that fresh water is injected from an inner-layer sleeve, and brine returns to the ground from an annular space between the inner-layer sleeve and an outer-layer sleeve; the reverse circulation cavity construction means that fresh water enters from an annular space between the inner-layer casing pipe and the outer-layer casing pipe, and brine returns to the ground from the inner-layer casing pipe, and both the two modes can be used for forming salt caverns.
S32: the mechanical integrity of the salt cavern gas storage is tested.
After the water-soluble cavity is completed, a mechanical integrity test is required to test the tightness of the salt cavern gas storage. The mechanical integrity test may employ conventional mechanical integrity test methods.
When the mechanical integrity test is carried out, the inner sleeve 13 is closed, nitrogen gas is injected into annular spaces of the technical sleeve 11 and the outer sleeve 12, or the nitrogen gas can be injected into the annular space between the inner sleeve 13 and the outer sleeve 12, the gas-water interface is pressed to a position 5-10 m below a technical sleeve shoe, and meanwhile, the gas pressure at the technical sleeve shoe is kept at a set pressure. The set pressure here is the theoretical upper limit operating pressure. During the test, the gas pressure at the shoe of the technical casing may drop, and the pressure can be increased by injecting brine into the well, so that the gas pressure at the shoe of the technical casing is kept at the set pressure. The depth of the gas-water interface is continuously recorded through an interface logging instrument, and parameters such as wellhead pressure, fluid flow, temperature and the like are continuously recorded through a ground detection instrument. And evaluating the sealing performance of the cavity according to the depth change value of the air-water interface. The mechanical integrity test time usually lasts for 24 hours, and the depth change of the air-water interface of the salt cavern gas storage in the test time is less than 1m, so that the mechanical integrity test is qualified. If the test fails, the set theoretical upper operating limit pressure needs to be lowered.
TABLE 1 mechanical integrity test detection data sheet
As shown in table 1, the mechanical integrity test started at day 18, month 2, 16 and ended at day 18, month 2, 17 for a total of 24 hours.
The gas pressure at the shoe of the technical casing is difficult to measure, the pressure at the wellhead is easy to measure, and the sum of the annular space pressure measured at the wellhead and the pressure of the gas column in the technical casing is the gas pressure at the shoe of the technical casing. The annular pressure can thus be measured during the mechanical integrity test, whereby the gas pressure at the shoe of the technical casing is obtained. The pressure of the air column in the technical casing can be calculated according to the depth of the pipe shoe of the technical casing.
Since the pressure of the gas column is substantially constant during the mechanical integrity test, the gas pressure at the shoe of the technical casing can be maintained at the set pressure by maintaining the annulus pressure measured at the wellhead at a fixed pressure value, for example 16.9MPa in this embodiment, so that the gas pressure at the shoe of the technical casing is maintained at 18.22 MPa.
According to the data in the table, the change of the gas-water interface depth of the salt cavern gas storage in the test time of 24 hours is less than 1m, so that the mechanical integrity test is qualified.
Because the pressure at the shoe of the technical casing in the salt cavern is much lower than the set pressure when the salt cavern is formed, the inner casing 13 can be closed before the mechanical integrity test is carried out, nitrogen is injected into the salt cavern, and the annular space pressure at the well head is increased to about 16.9 MPa.
S33: and (4) carrying out numerical simulation on the shape change of the cavity of the salt cavern gas storage to detect the stability of the salt cavern gas storage.
The method can be used for carrying out numerical simulation by utilizing geomechanics, rock rheology theory and finite element theory to detect the stability of the salt cavern gas storage. The deformation amount, the volume shrinkage rate and the shear expansion safety coefficient of the salt cavern gas storage change in the process that the salt cavern gas storage operates for 30 years at the theoretical operation upper limit pressure.
The shear-expansion safety coefficient can be according to the formula:
calculation of where SFvsTo secure the shear-expansion coefficient, I1Is a first principal stress invariant, I1＝σ1+σ2+σ3，J2Is the second principal stress invariant offset, J2＝1/6[(σ1-σ2)2+(σ2-σ3)2+(σ3-σ1)2]，σ1、σ2、σ3The maximum principal stress, the minimum principal stress and the vertical principal stress of the stratum where the technical casing pipe shoe is located are respectively adopted.
The deformation does not exceed the safety critical value of the industrial standard, the volume shrinkage rate does not exceed 10%, and the shear expansion safety coefficient is 2-3, so that the stability is qualified.
If the stability of the salt cavern gas storage is not qualified, the theoretical operation upper limit pressure needs to be reduced. After the stability of the salt cavern gas storage is qualified, a numerical value smaller than the theoretical operation upper limit pressure is used as the current operation upper limit pressure before the salt cavern gas storage is put into production, and the operation pressure of the salt cavern gas storage is controlled within a range not exceeding the current operation upper limit pressure in the current formal production. The current operation upper limit pressure is generally set empirically, and may be generally set to 80% to 95% of the theoretical operation upper limit pressure. The current operation upper limit pressure may be set to 17Mpa, for example, when the theoretical operation upper limit pressure is 18.22 Mpa.
After the salt cavern gas storage is established, the operation upper limit pressure of the salt cavern gas storage can be determined by the determination method of the operation upper limit pressure of the salt cavern gas storage shown in fig. 1. The current operation upper limit pressure set according to experience at present is much smaller than the theoretical operation upper limit pressure, so that the storable amount of the salt cavern gas storage is smaller. The operation upper limit pressure of the salt cavern gas storage determined by the method shown in fig. 1 is higher than the current operation upper limit pressure set according to experience, so that the storable amount of the salt cavern gas storage can be increased.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A method of determining an upper operating pressure for a salt cavern gas storage, the method comprising:
determining target operation of salt cavern gas storageLimiting pressure P1，P2≤P1≤P0，P0Is the theoretical upper limit pressure, P, of operation of the salt cavern gas storage2The current operation upper limit pressure of the salt cavern gas storage is set;
monitoring the actual operating pressure of the salt cavern gas storage;
injecting gas into the salt cavern gas storage until the actual operation pressure of the salt cavern gas storage is gradually increased to the target operation upper limit pressure P1；
Carrying out microseism monitoring through a monitoring well to obtain the number of microseism events occurring every day in a first pressure lifting stage and the number of microseism events occurring every day in a second pressure lifting stage, wherein the first pressure lifting stage is from the actual operating pressure of the salt cavern gas storage to P2The second pressure raising stage is that the actual operating pressure of the salt cavern gas storage is from P2Increase to P1The depth of the monitoring well reaches a salt layer where the salt cavern gas storage is located;
comparing the average number of microseismic events per day n occurring during the first pressure rise period1And the number n of microseismic events that occur on average per day during the second pressure build-up phase2；
When n is2And n1When the ratio of (A) to (B) is less than a preset value, determining the upper limit pressure of the salt cavern gas storage operation as P1。
2. The method of determining of claim 1, wherein the performing microseismic monitoring via monitoring wells comprises:
arranging multistage three-component detectors in the monitoring well, wherein the multistage three-component detectors are distributed upwards at equal intervals from the bottom of the monitoring well;
and monitoring the microseism event through the multistage three-component detector.
3. The method of claim 1, wherein the injecting gas into the salt cavern reservoir is performed until the gas is injected into the salt cavern reservoirGradually increasing the operating pressure of the salt cavern gas storage to a target operating upper limit pressure P1The method comprises the following steps:
raising the actual operating pressure of the salt cavern reservoir to P at a first rate during the first pressure raising phase2；
Raising the actual operating pressure of the salt cavern reservoir at a second rate from P in the second pressure-raising phase2Is lifted to P1The first speed is greater than the second speed.
4. The determination method according to claim 3, wherein a ratio of the first speed to the second speed is 2 to 3.
5. The method of determining as claimed in claim 1 wherein said monitoring actual operating pressure of said salt cavern reservoir comprises:
monitoring the wellhead gas injection pressure of the salt cavern gas storage;
and acquiring the gas column pressure of the salt cavern gas storage, and taking the sum of the wellhead gas injection pressure and the gas column pressure as the operating pressure of the salt cavern gas storage.
6. The method of claim 1, wherein the predetermined value is greater than 100% and less than 110%.
7. The determination method according to any one of claims 1 to 6, characterized in that the theoretical upper limit operating pressure is determined by:
carrying out an earth stress test in an injection well of the salt cavern gas storage;
determining the relation between the minimum principal stress and the formation depth according to the data obtained by the geostress test;
and determining the theoretical operation upper limit pressure of the salt cavern gas storage according to the relation between the minimum principal stress and the formation depth.
8. The method of claim 7, wherein the performing geostress testing in the injection and production well of the salt cavern reservoir comprises:
and acquiring the minimum principal stress of a plurality of depth positions by adopting a hydraulic fracturing method.
9. The method of claim 8, wherein determining the minimum principal stress versus formation depth from the data from the geostress test comprises:
and fitting a relation curve of the minimum principal stress and the depth according to the depth values of the plurality of depth positions and the minimum principal stress of the plurality of depth positions.
10. The method of any one of claims 1 to 6, further comprising, prior to performing microseismic monitoring via the monitoring wells to obtain the number of microseismic events occurring per day during the first pressure rise period and the number of microseismic events occurring per day during the second pressure rise period:
recording the position of each occurrence of the micro-seismic event in a plane coordinate mode, judging whether the micro-seismic event is caused by the increase of the pressure in the salt cavern gas storage, and removing the micro-seismic event when the micro-seismic event is not caused by the increase of the pressure in the salt cavern gas storage.
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| CN113738446B (en) * | 2020-05-28 | 2023-12-22 | 中国石油天然气股份有限公司 | Method for rebuilding air storage in salt cavern |
| CN112362475B (en) * | 2020-11-09 | 2022-05-10 | 重庆科技学院 | Evaluation method for trapped sealing ultimate pressure of oil reservoir type gas storage |
| CN115142831B (en) * | 2022-06-23 | 2024-04-26 | 江苏国能石油天然气有限公司 | Method for driving MVR to produce salt by utilizing residual brine pressure of salt cavern gas storage |
| CN115450585A (en) * | 2022-09-09 | 2022-12-09 | 中国科学院武汉岩土力学研究所 | Sediment type salt cavern compressed air energy storage method, monitoring method and energy storage system |
| CN117233835B (en) * | 2023-09-18 | 2024-05-28 | 北京戎彩科技有限公司 | Method for optimizing operation pressure interval of underground gas storage by microseism monitoring technology |
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